Modern spark ignition internal combustion engines typically require high ignition spark energy to initiate combustion. It has been found that a high initial secondary current from the ignition coil to the spark plug is beneficial for robust combustion initiation. It has also been found that a long duration spark caused by a lower secondary current is needed for enhanced repeatability (e.g. poor timing of air-fuel mixture). One approach to solving this problem has been using two ignition coils and combining the coil outputs while isolating the ignition coils from each other using high voltage diodes. Another problem with the delivery of very high spark energy is spark plug electrode wear. The dual coil system allows disabling one of the coils when not needed in order to reduce spark plug electrode erosion. Also, the electrode erosion of the full output of the dual coil system is less than a traditional system with the same peak secondary current and burn time since the combined output of the two coils yields a concave secondary current waveform that has a lower secondary current over time than the typical triangular waveform. Electrode erosion is proportional to this integral secondary current. A drawback of the dual coil system is additional cost of another ignition coil and two high voltage blocking diodes. Another concern with the dual coil system is unknown durability, due to the inclusion of high voltage blocking diodes.
The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also be inventions.